Various types of separation media are available for use in isolating target substances in chemical or biological samples. In molecular biology, various materials are used in fractionation procedures, including agarose and polyacrylamide in electrophoretic fractionation, and gel permeation, ion exchange and affinity materials for chromatography. Among such materials, both organic polymer and silicon-based particles find use in separations of targets such as nucleic acids. In each type of separation there is a need at some point physically to remove a liquid phase from the particles in the solid phase. This may be achieved by immobilising the particles, for example in the form of a column or on a gel plate, and eluting the liquid phase or by aggregating the particles by applying a force under centrifugation or using magnetism. The use of magnetism to separate particles from other sample components requires the particles to respond to a magnetic field. Because organic or silicon-based materials are not themselves magnetically responsive, there is a need to devise methods of production of magnetic particles which incorporate both a magnetic component and a polymer component.
WO83/03920 describes preparation of polymer magnetic particles in which iron is introduced into porous polymer particles in solution. Non-magnetic iron salts are mixed with the porous particles and the iron is subsequently precipitated in the pores as magnetite deposits. In order to achieve this, there is a requirement that an additional step comprising an oxidation reaction be carried out in situ to convert the non-magnetic iron into magnetite.
More recently, U.S. Pat. No. 5,648,124 describes a process for preparing magnetically responsive micro particles which are presently available commercially from Seradyn Inc. According to this process, a non-porous core particle is provided onto which is deposited magnetite from a ferrofluid in the presence of a heterocoagulant. A coating of magnetite is deposited on the surface of the core. In order to achieve a sufficiently high concentration of magnetite, there is a need in this process to use the heterocoagulant, which acts as a binding agent to enable further magnetite to be deposited on the coated core. The particles obtained by this process have a further disadvantage that the magnetic component therein is not uniformly distributed.
The present invention aims to overcome the drawbacks of the prior art by providing a simplified process for the production of useful polymer magnetic particles.